Idiotypes are serological markers of antibody variable (V) regions which allow study f the antibody repertoire and also can be used for specific manipulation of immunity. We are studying antibody responses to Ia.7, with the goal of understanding V region expression in this response. In addition, we are studying induction of anti-Ia.7 antibody responses by anti-idiotype in vivo, as a model for vaccination. Specific projects: 1) A new project is the use of sequential immunizations with different mAbs of the anti-Ia.7 family, to focus the anti-idiotypic response on the cross- reactive idiotype (CRI). The goal is to derive mouse reagents (polyclonal and monoclonal) reactive with the CRI, to characterize induced populations for expression of this marker, and if possible to derive an internal image of Ia.7. Preliminary results indicate responses to the CRI in mice immunized sequentially, and fusions are in progress to derive monoclonal anti-idiotopes. In related work, we have studies the antibody populations induced by in vivo treatment with monoclonal anti-idiotopes, and shown that they all express the cross-reactive idiotype (CRI) detected by xenogeneic anti-Id. 2) We are continuing to study novel idiotype-carrier conjugates. In order to avoid damage to the variable region possible with other protein conjugation procedures, carbohydrate sites of the constant region were biotinylated using hydrazide. Western blots developed with avidin- peroxidase showed that, as desired, biotin was incorporated on the heavy chain but not on the light chain. Enzyme digestion of the Ig is being used to further map the biotin sites to the Fc fragment. 3) A study of antibody diversity by sequencing of heavy and light chain variable regions of anti=Ia.7 hybridomas is continuing under a contract with the lab of Dr. Tom Wood, FCRF.